<strong>
<%@ page contentType="image/jpeg" import="java.util.*,java.awt.*,java.io.*,java.awt.image.*,javax.imageio.*" pageEncoding="utf-8"%>  
<%!  
Color getRandColor(int fc,int bc){//给定范围获得随机颜色  
Random random = new Random();  
if(fc>255) fc=255;  
 if(bc>255) bc=255;  
 int r=fc+random.nextInt(bc-fc);  
 int g=fc+random.nextInt(bc-fc);  
 int b=fc+random.nextInt(bc-fc);  
 return new Color(r,g,b);  
 }  
 %>  
 <%  
 //设置页面不缓存  
 response.setHeader("Pragma","No-cache");  
 response.setHeader("Cache-Control","no-cache");  
 response.setDateHeader("Expires", 0);  
   
 // 在内存中创建图象  
 int width=60, height=20;  
 BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);  
    
 // 获取图形上下文  
   Graphics g = image.getGraphics();  
     
   //生成随机类  
   Random random = new Random();  
     
   // 设定背景色  
   g.setColor(getRandColor(200,250));  
  g.fillRect(0, 0, width, height);  
     
  //设定字体  
  g.setFont(new Font("Times New Roman",Font.PLAIN,18));  
    
   //画边框  
   //g.setColor(new Color());  
   //g.drawRect(0,0,width-1,height-1);  
    
   // 随机产生155条干扰线，使图象中的认证码不易被其它程序探测到  
   g.setColor(getRandColor(160,200));  
   for (int i=0;i<155;i++)  
   {  
  int x = random.nextInt(width);  
   int y = random.nextInt(height);  
   int xl = random.nextInt(12);  
  int yl = random.nextInt(12);  
   g.drawLine(x,y,x+xl,y+yl);  
   }  
     
   // 取随机产生的认证码(4位数字)  
   String sRand="";  
  for (int i=0;i<4;i++){  
   String rand=String.valueOf(random.nextInt(10));  
   sRand+=rand;  
   // 将认证码显示到图象中  
  g.setColor(new Color(20+random.nextInt(110),20+random.nextInt(110),20+random.nextInt(110)));// 调用函数出来的颜色相同，可能是因为种子太接近，所以只能直接生成  
   g.drawString(rand,13*i+6,16);  
   }  
     
   // 将认证码存入SESSION  
   session.setAttribute("rand",sRand);  
    
   // 图象生效  
   g.dispose();  
   OutputStream output=response.getOutputStream();  
    
   // 输出图象到页面  
  ImageIO.write(image, "JPEG", response.getOutputStream());  
  output.flush();  
   out.clear();  
   out = pageContext.pushBody();  
     
 %>  
</strong>  